1. Field of the Invention
The present invention relates to a method and apparatus for processing a semiconductor substrate by use of a plasma, and more particularly to a plasma processing of a semiconductor substrate with energy supplied.
2. Description of the Related Art
Integration density of an integrated circuit as a main device of microelectronics has been increased. With the increase of the integration density, a pattern width becomes narrower so that the processing such as etching and deposition to a semiconductor substrate with large irregularity is required. To fill the above-mentioned requirement, there are provided a lot of methods of processing of a semiconductor device by use of plasma.
For example, a plasma etching method at a low pressure (under high vacuum) has been developed as an etching technique for a thin film (Japanese Laid Open Patent Applications: JP-A-Showa 61-256727, JP-A-Showa 62-194623, JP-A-Heisei 5-247673, and JP-A-Heisei 6-132252). In these conventional techniques, various dry etching apparatuses are used such as a plasma etching apparatus, a sputtering apparatus, an electron cyclotron resonance (ECR) etching apparatus, a magnetron etching apparatus, and an ion beam etching apparatus. An etching rate increases by employing a gas containing halogen such as Freon based gas (for example, CF4 and the like) during processing of a semiconductor substrate by a dry etching method using plasma. Consequently, a fine pattern processing can be realized. Also, in a thin film deposition technique, a halogen based gas such as TiCl4, WF6 is dissociated, and the deposition at a low temperature and at a high rate can be realized.
However, there has been limitations in processing precision, when the etching for fine patterns is performed, or a film is deposited on a micro-processed irregular surface.
First, a problem of the fine pattern etching will be described below. For example, when contact holes are formed in an SiO2 insulating film of a semiconductor device by an etching method, the limitation of a selection ratio is known to be about 50 when an etching rate is kept at a value not less than 1 xcexcm/min. Here, the selection ratio is a ratio of an etching rate to a SiO2 film formed on a silicon substrate or a nitride film to an etching rate of the silicon substrate or the nitride film.
That is, when the contact holes are formed, over-etching is performed to completely open the holes in consideration of the deviation of processes. This means that the silicon substrate or the nitride film is simultaneously etched away by {fraction (1/50)} of the thickness of the SiO2 film. As a result, the silicon substrate is inevitably etched away to some extent.
In the semiconductor device such as a metal oxide semiconductor large-scale integrated device (MOSLSI device), there arises a problem in which a silicon substrate is etched to a p-n junction layer which has been formed under the contact hole in conjunction with the increase of the integration density. For this reason, new countermeasures such as deposition of a polymer on the silicon substrate or a nitride film using a fluorocarbon gas are required.
The reason in which a satisfactory selection ratio can not be attained will be described below. Let""s consider a case where an etching process is performed at a high rate by use of a high density plasma. When a C4F8 gas plasma is generated, radicals and CxFy+ ions having high energy are generated in the plasma through a complex dissociation process such as C4F8xe2x86x92C4F7xe2x86x92C3F5xe2x86x92C2F4xe2x86x92CF2xe2x86x92CF xe2x86x92C+F. In the plasma, electron energy is not less than about 5 eV, which is relatively high. Therefore, a dissociation rate of the C4F8 gas becomes high. Thus, radical species such as CF2 are rare which act as a precursor necessary for obtaining a high selection ratio. Therefore, an important problem is that desired radical species or desired ion species are selectively generated.
To address the above-described problem, there is disclosed conventional methods in which electron energy is reduced in a low pressure and high density plasma (Japanese Laid Open Patent Applications: JP-A-Heisei 5-029613, and JP-A-Heisei 6-122978). In these methods, dissociation in the plasma is relatively restrained, and a lot of radicals contributing to an improvement in selectivity are generated, compared with the conventional methods. However, a problem is remaining in that an ion current density injected into a semiconductor substrate is reduced and the etching rate is also reduced, since an amount of high-energy electrons which contribute to ionization is relatively small. On the other hand, there is known a method in which a plasma is generated by supplying electrons whose energy is controlled by an electron beam. In this method, although dissociation and ionization can be accurately controlled, ionization requiring high energy and dissociation requiring low energy cannot simultaneously occur. Also, a plasma having a high density cannot be homogeneously generated across a large diameter. As a result, there gives rise to problems for practical use.
Next, deposition on an irregular surface of a semiconductor substrate will be described below. For example, when a thin film is deposited on the semiconductor substrate by use of a UHF plasma using a C4F8 gas as a process gas, it is preferable that a lot of CF radicals are generated. In such a case, low permittivity, high heat resistance, and superior embedding property are attained. However, in the above-described UHF plasma, CF2 and CF3 are mainly generated, so that satisfactory properties are not accomplished.
In conjunction with the above description, a dry etching apparatus is described in Japanese Laid Open Patent Application (JP-A-Showa 62-76627). In this reference, a gas inside a chamber is exhausted by an exhausting unit. Then, a reactive gas is introduced into a chamber. A power is applied between opposing parallel plate electrodes to generate a discharge between the electrodes. A sample is located on one of the opposing electrodes. An electron beam is supplied into a discharge plasma generated between the electrodes. In this dry etching apparatus, however, a parallel plate electrode structure is adopted. Therefore, an electron energy distribution is broad. As a result, it is difficult to apply the apparatus to a very fine pattern processing.
Also, a plasma reacting apparatus is described in Japanese Laid Open Patent Application (JP-A-Showa 64-90534). In this reference, opposing parallel plate electrodes are provided in a chamber and a plasma is generated between the electrodes. An electron beam is supplied between the electrodes. Thus, etching or deposition is performed to a substrate located on one electrode.
Also, a dry etching apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 4-181727). In this reference, an etching gas is introduced in a chamber, and opposing electrodes are provided in the chamber. A high frequency power is applied to the electrodes to cause a glow discharge to generate a plasma. An electron gun outputs an electron beam toward the electrodes and the electron beam is scanned on the semiconductor wafer.
Also, a plasma surface processing apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 6-181185). In this reference, an electron beam is irradiated to a plasma source gas to generate a plasma. At this time, an electron distribution of electrons irradiated is modulated with respect to space and time. A high frequency bias is applied to a wafer holder in synchronous with the modulation so that the plasma is modulation with respect to time. Thus, a semiconductor wafer is etched.
Also, an electron beam exciting plasma film forming apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 8-27577). In this reference, two electron beams with high energy and low energy are provided. A plasma is generated through excitation by the electron beam. When the electron beam with high energy is irradiated, a plasma PBa composed of gas molecules which require high activation energy for ionization or dissociation is generated. When the electron beam with low energy is irradiated, a plasma PBb composed of gas molecules which require low activation energy for ionization or dissociation is generated. The respective plasma are used to perform chemical vapor deposition on a sample for formation of a multi-element thin film.
Also, a plasma CVD apparatus is described in Japanese Laid Open Patent Application (JP-A-Heisei 8-13151). In this reference, an electron beam gun is provided concentrically to a plasma generating region. A mixture gas which is difficult to be ionized is introduced from a port close to an acceleration electrode and a mixture gas which is easy to be ionized is introduced from a port apart from the acceleration electrode. A probe detects generated ions and radicals to feedback the detecting result to the acceleration power supply for controlling the energy of electron beam. A current of an inverse magnetic field coil is controlled to cancel the magnetic field.
Also, a method of manufacturing a fine crystal film is described in Japanese Laid Open Patent Application (JP-A-Heisei 9-260292). In this reference, a row material gas introduced into a reaction chamber is kept at the pressure of 0.5 to 50 mTorr. The row material gas is set to a plasma state by use of electrons accelerated by an electron beam gun such that ions or radicals are deposited on a substrate.
Therefore, an object of the present invention is to provide a method and apparatus for plasma processing, in which an electron beam is injected into a plasma to a control an electron energy distribution.
In order to achieve an aspect of the present invention, in a plasma processing method, a plasma is generated using a process gas, and an electron beam is injected into the plasma to control an electron energy distribution in the plasma. Then, a semiconductor substrate is processed using the plasma with controlled electron energy distribution.
The plasma is generated by a high frequency signal of 300 MHz or above.
The process gas preferably is such a gas as halogen radicals and halogen ions can be generated from the process gas in the plasma, and contains at least one gas selected from the group consisting of CF4, C4F8, CHF3, C2F6, Cl2, HBr and BCl3. The process gas may further contain a gas used to control kinds of and densities of the halogen radicals and halogen ions to be generated. For example, the process gas further contains at least one gas selected from the group consisting of O2, H2, N2, He, Ar and Xe. The process gas may be a gas, from which radicals as precursor can be generated. For example, the process gas contains at least one gas selected from the group consisting of CH4, C2F4, SiH4, AlCl3, TiCl4 and WF4.
The plasma is one of UHF plasma, ECR plasma, induction coupling plasma and helicon wave plasma.
It is preferable that the energy of the electron beam is controlled depending upon a kind of active species to be generated, and the electron beam has energy in a range of 1 to 100 eV.
The electron beam may be modulated with respect to time or pulse-modulated. In this case, a pulse energy height of the modulated electron beam is controlled depending upon a kind of first active species to be generated, and a time period of a pulse is shorter than a life time of second active species, which should exist together with the first active species.
When the electron beam includes first and second types of electron beams, the first and second types electron beams may be separately pulse-modulated. Thus, a pulse energy height of the first type of modulated electron beam is controlled depending upon a kind of first active species to be generated, and a time period of a pulse is shorter than a life time of second active species, which should exist together with the first active species. Also, a pulse energy height of the second type of modulated electron beam is controlled depending upon a kind of third active species to be generated, and a time period of a pulse is shorter than the life time of the second active species and a life time of fourth active species, whereby the first to fourth active species coexist in the plasma.
In order to achieve another aspect of the present invention, a plasma processing method includes:
generating plasma using a process gas; and
injecting an electron beam into the plasma to produce desired active species in the plasma, wherein the desired active species are used for processing a semiconductor substrate.
In order to achieve still another aspect of the present invention, a plasma processing apparatus includes a chamber, plasma generating antennas, an electron beam source section and a control unit. The plasma generating antennas generates a plasma in the chamber in response to a signal, using a process gas. The electron beam source section includes at least one electron beam source and injects an electron beam group into the plasma to control an electron energy distribution in the plasma. The control unit controls an energy of the electron beam group. Thus, a semiconductor substrate located in the chamber is processed using the plasma with controlled electron energy distribution.
The plasma generating antennas may be provided in the chamber, or outside the chamber.
Also, the electron beam source section may be provided on sides of the chamber, or on an upper portion of the chamber.
The control unit control controls the electron beam source section such that the electron beam is modulated with respect to time. Instead, the control unit control may control the electron beam source section such that the electron beam is pulse-modulated. In this case, a pulse energy height of the modulated electron beam is controlled depending upon a kind of first active species to be generated, and a time period of a pulse is shorter than a life time of second active species, which should exist together with the first active species.
Also, when the electron beam source section includes a plurality of electron beam sources, the control unit control may control the electron beam source section such that first and second types of electron beams are irradiated, the first and second types electron beams are pulsemodulated. In this case, a pulse energy height of the first type of modulated electron beam is controlled depending upon a kind of first active species to be generated, and a time period of a pulse is shorter than a life time of second active species, which should exist together with the first active species. Also, a pulse energy height of the second type of modulated electron beam is controlled depending upon a kind of third active species to be generated, and a time period of a pulse is shorter than the life time of the second active species and a life time of fourth active species, whereby the first to fourth active species coexist in the plasma.